Unit 7 - Magnets & Electromagnetism Flashcards
At which part of a magnet are the
magnetic forces strongest?
The poles of the magnet.
What happens when two magnets are
brought close to each other?
They exert a force on each other.
What type of force is exerted if two like
poles of a magnet are brought near each
other?
A repulsive, non-contact force.
What type of force is exerted if two unlike
poles of a magnet are brought near each
other?
An attractive, non-contact force.
What is the difference between a
permanent magnet and an induced
magnet?
● A permanent magnet produces its own
magnetic field
● An induced magnet becomes magnetic
when placed in a magnetic field
What type of force does induced
magnetism always cause?
A force of attraction.
What happens when an induced magnet
is removed from a magnetic field?
The induced magnet loses most/all of its
magnetism.
What is a magnetic field?
The region surrounding a magnet where
another magnet or magnetic material
experiences a non-contact force.
Give four examples of magnetic
materials
- Iron
- Steel
- Cobalt
- Nickel
What can always be said about the force
between a magnet and a magnetic
material?
It is always attractive.
How does the strength of a magnetic
field alter as you move further away from
the magnet producing it?
The magnetic field strength decreases
the further you move away.
In what direction does a magnetic field
point?
● In the direction that a north pole would
experience a force if placed in the field
● From the north seeking pole to the
south seeking pole of a magnet
What does a magnetic compass
contain?
A small bar magnet that points in the
direction of the Earth’s magnetic field.
What is produced when current flows
through a conducting wire?
A magnetic field is produced around the
wire.
What determines the strength of the
magnetic field around a current-carrying
wire?
● The magnitude of the current flowing
through the wire
● The distance from the wire
What is a solenoid?
A coil of wire which when current passes
through creates a strong magnetic field.
Describe the magnetic field found inside
a solenoid.
Strong and uniform.
What is an electromagnet?
● A solenoid with an added iron core
● Adding the iron core increases the
strength of the magnetic field
What is the motor effect?
When a force is exerted between a
magnetic field and a current-carrying
conductor placed in that field.
What rule is used to determine the force
experienced due to the motor effect?
Fleming’s Left-Hand Rule
When using Fleming’s left hand rule
what does the forefinger represent?
The forefinger points in the direction of
the magnetic field.
When using Fleming’s left hand rule
what does the second finger represent?
The second finger points in the direction
of current flow in the conductor.
What factors affect the size of the force
on a current-carrying wire in a magnetic
field?
● The magnitude of the current flowing
through the conductor
● The strength of the magnetic field that
the conductor is placed in
If the direction of current in a
current-carrying wire placed in a uniform
magnetic field is reversed, what happens
to the force?
The direction of the force is reversed.
If the strength of the current in a
current-carrying wire placed in a uniform
magnetic field is increased, what
happens to the force?
The strength of the force is increased.
What criteria must be met for the
equation linking force, magnetic flux
density, current and length to hold?
The conductor must be at right-angles to
the magnetic field it is placed in.
What is the unit used for magnetic flux
density?
Tesla, T
How does an electric motor work?
● A coil of wire, carrying a current, is placed in a magnetic field
● The forces on the two sides perpendicular to the field experience forces in opposite directions
● This causes a rotational effect
How do loudspeakers make use of the
motor effect?
The motor effect is used to convert
variations in the current of an electrical
circuit into the pressure variations which
produce audible sound.
Explain how a loudspeaker works.
● A cone with a wire wrapped around it is connected to an
a.c power supply and is placed in a permanent
magnetic field
● When current flows through the wire, it creates a
second magnetic field, which interacts with the
permanent field
● This produces a force which causes the cone to vibrate
How is the pitch of the sound from a
loudspeaker changed?
● The frequency of the a.c current is
altered
● This creates a different frequency of
vibration in the cone
